There have been many attempts at using tracers to characterize hydrocarbon wells, the most relevant being discussed in brief below.
Present methods for detecting water intrusion include the use of fluorescent materials, radioactive materials, peptides and amino acids amongst others. However these compounds are not always easily detectable in low concentrations.
WO0181914 concerns a method for monitoring the hydrocarbon and water production from different production zones in a hydrocarbon reservoir or injection wells and detection of different phenomena such as e.g. local variations in pH, salinity, hydrocarbon composition, temperature, pressure, micro organisms, and the difference/ratio between production of formation and/or injection water from various zones in a hydrocarbon reservoir. The method comprises dividing regions around wells in the reservoir into a number of sections, and injecting or placing specific tracers with unique characteristics for each section into the formation in these regions. The tracers are chemically immobilized/integrated in the formation or in constructions/filters around the wells, the tracers (tracer carriers) being chemically intelligent and released as a function of specific events. Detecting the tracers after the entry point, provides information about the various zones. There is solely mention of PEG-materials being part of the carrier material.
U.S. Pat. No. 4,555,489 describes a method for determining flow patterns within a subterranean formation penetrated by a spaced apart injection system and production system that comprises injecting into the formation at a predetermined depth from the injection system a solution containing a small amount of one or more water-soluble tracer compounds, recovering said tracer in the production system, determining the depth of recovery, and identifying said tracer compounds by gas chromatography and flame ionization detector; said tracer compounds being water-soluble organic compounds having phosphorus, nitrogen, or sulphur in the molecule.
WO2007132137 describes a method for the characterization of hydrocarbon reservoirs using biological tags.
U.S. Pat. No. 5,077,471 describes a method wherein formation fluid flows in earth formations opposite a perforated well bore zone are measured and monitored by injecting radioactive tracers into the perforations, blocking the perforations to retain the tracers in the formation, monitoring the apparent decay rates of the injected tracers, and then determining the rate at which the tracers are being carried away by fluid movements in the formation. From this the flow rate of the fluids in the earth formations adjacent the borehole interval is inferred.
U.S. Pat. No. 6,670,605 describes a method wherein a formation fluid analysis module utilizes a down-hole mass spectrometer to determine the molecular constituents of formation fluids, as distinguished from drilling contaminants, and to provide information about the physical and chemical properties of the sample.
U.S. Pat. No. 5,789,663 describes a method for quantitatively measuring the characteristic physical parameters of a porous medium, such as an aquifer that is initially recharged at a recharge rate and subsequently discharged at a discharge rate by a pumped fluid utilizing a single well into which a tracer is injected during recharge, and at which the tracer is subsequently detected during discharge. A measurement of the elapsed time, together with a formula based on a convective physical model relating the characteristic parameters to the time measurements is provided.
The use of PEG tracers has to some degree been discussed in various journals. Analytica Chimica Acta Volume 611, Issue 2, “A solid-phase extraction and size-exclusion liquid chromatographic method for polyethylene glycol 25 p-aminobenzoic acid determination in urine: Validation for urinary excretion studies of users of sunscreens” for instance describes the detection of a PEG derivate in sunscreen such that the detection of sunscreen levels in human urine is allowed. However PEG compound is not used as a tracer, it is a naturally occurring compound in the sunscreen.
Commercially available polymer products are usually prepared in a way that gives a broad range of molecular weight. Molecular weight can be measured as an average by weight or number and the ratio between these, Mw/Mn, s called the breath of the distribution. Most polymers made by free-radical or coordination polymerization of vinyl monomers have ratios from 2 to about 10, while very highly branched polymers like polyethylene made by free-radical, high pressure processes, will have ratios of 20 and more.
Poly ethylene glycol (PEG) is the most commercially important type of polyether. Polypropylene glycol (PPG) is another polyether with many properties in common with PEG. PEG has the following structure, HO—(CH2—CH2—O)n—H . Most PEGs include molecules with a distribution of molecular weights, i.e. they are polydisperse. The abbreviation (PEG) is usually termed in combination with a numeric suffix, such as “PEG 300” which indicates the average molecular weights. For an illustration of such a polydisperse PEG, please see FIG. 1 attached, which is a full scan mass spectrum of “PEG 300” simplified from J. Zhang, Int. J. of Pharm. 282, pp. 183-187. FIG. 1 shows the composition and distribution of PEG 300, having an average molecular weight of 300, which mostly includes oligomers represented by n=5 to 9. Products are commercially available as PEG 200, 300, 400 etc up to more than 20000.
US 2006/0154297 from Gauchel, “Marker substance and the use of the same in diagnostic methods”, teaches a method for using PEG markers as non-metabolisable marker substances together with a metabolisable substance in a diagnostic method related to e.g. drug-addicted patients. The two different types of markers present in a drinkable solution, is administrated to the patient followed by analysis of the urine taken after 60 minutes. The method further describes analysis of the urine sample by use of a HPLC chromatographic separation in combination with RI detection of the PEG fraction followed by UV detection of the metabolisable marker. Throughout the application Gauchel refers to the “PEG-marker” in plural form implicating use of polydisperse PEG's/PEG fractions. This is clearly seen by use of terms as “added to non-metabolisable marker substances”, together with PEG markers” and “containing 1-3 g PEG marker mixture”. A chromathogram of PEG 300 shown in FIG. 2 of Gauchel clearly indicates that this PEG substance constitutes of more than 9 different PEG oligomers of different molecular weights. Gauchel also refers to use of “monodisperse PEG fractions”. Thus Gauchel uses the term “monodisperse” somewhat differently from what is used in polymer chemistry.
US patent application US 2006/0008850 A1 describes a method for generating a library of monodisperse PEG derivatives. This method of using “combinatorial chemistry or combinatorial synthesis” is a well known technique and is a general approach for generating a large number of different molecules, e.g. for making peptide libraries. The same approach for generating functionalized PEG's with both hydrophilic and hydrophobic end groups is also mentioned. The libraries so formed are used for screening the effect of PEG length, functional end groups and type of drug attached to the PEG moiety in order to isolate potent substances for use as therapeutics.
Thus, none of the abovementioned applications describe the novel tracer material comprising generally monodisperse polyether alcohols for marking and low concentration detection as will be described below. In order to distinguish the compounds of the present invention from the actually non-monodisperse or polydisperse polyether alcohol compounds of the background art, we have chosen to use the term truly monodisperse when describing the polyether alcohol compounds.